1. Field of Invention
The present invention relates to an electro-optical device and a method of driving the same, an organic electroluminescent display device using (electroluminescence) elements, and an electronic apparatus having an electro-optical device or an organic electroluminescent display device. The invention is particularly intended to achieve a reduction in power consumption with a simple circuit structure.
2. Description of Related Art
Currently, electro-optical devices that display data which are incorporated in electronic apparatuses can include a liquid crystal display device, an electrophoresis device, and an organic electroluminescent display device. The organic electroluminescent display device can be constructed using organic electroluminescent elements that are electro-optical elements. FIG. 16 shows the structure of a conventional organic electroluminescent display device 10. FIG. 16 illustrates only portions corresponding to four data lines X1 to X4 and two scan lines Y1 and Y2 in the organic electroluminescent display device 10.
The organic electroluminescent display device 10 includes a plurality of data lines X1 to X4 which extend in the column direction, a plurality of scan lines Y1 and Y2 which extend in the row direction, and common feeder lines 11 extending in parallel to the data lines X1 to X4 and having first ends connected to a power supply VDD. Organic electroluminescent elements 12 which function as color-emitting units are disposed correspondingly to intersections of the data lines X1 to X4 and the scan lines Y1 and Y2. In this example, the organic electroluminescent elements 12 capable of emitting red (R), the organic electroluminescent element 12 capable of emitting green (G), and the organic electroluminescent element 12 capable of emitting blue (B) are in turn associated with the data lines X1 to X4 in such a manner that the first data line X1, the second data line X2, the third data line X3, and the fourth data line X4 correspond to R, G, B, and R, respectively. Three dots including an organic electroluminescent element 12 capable of emitting red, an organic electroluminescent element 12 capable of emitting green, and an organic electroluminescent element 12 capable of emitting blue which are aligned in the row direction constitute one pixel P, allowing the organic electroluminescent display device 10 to achieve a color display.
The cathode side of each of the organic electroluminescent elements 12 is grounded, while the hole injection side thereof is connected to the common feeder line 11 via a p-channel thin film MOS transistor (hereinafter, referred to as PMOS transistor) 13. The gates of the PMOS transistors 13 are connected to the associated data lines X1 to X4 via n-channel thin film MOS transistors (hereinafter referred to as NMOS transistors) 14, and holding capacitances 15 are interposed between the gates of the PMOS transistors 13 and the common feeder lines 11. The gates of the NMOS transistors 14 are connected to the associated scan lines Y1 and Y2. The organic electroluminescent elements 12, the PMOS transistors 13, the NMOS transistors 14, and the holding capacitances 15 constitute a so-called active matrix display screen 20.
First ends of the scan lines Y1 and Y2 are connected to a scan line driving circuit 30. The scan line driving circuit 30 includes a shift register 31 and a buffer 32, in which outputs of the shift register 31 are fed to the scan lines Y1 and Y2 via the buffer 32. In synchronization with the shift operation of the shift register 31, therefore, the plurality of scan lines Y1 and Y2 are selected in turn to each repeat charging and discharging.
On the other hand, first ends of the data lines X1 to X4 are connected to a data line driving circuit 40. The data line driving circuit 40 includes a shift register 41, and a plurality of switching elements 42 corresponding to the data lines X1 to X4, in which outputs of the shift register 41 are fed to the switching elements 42. In synchronization with the shift operation of the shift register 41, therefore, the switching elements 42 are selected in turn to be each repeatedly turned on (conduct) and off (interrupt).
The side of each of the switching elements 42 which is opposite to the data lines X1 to X4 is connected to one of video signal lines 17R, 17G, and 17B. The video signal lines 17R to 17B are signal lines which supply analog video signal voltages VIDR, VIDG, VIDB corresponding to red (R), green (G), and blue (B), and are adjacent to the display screen 20, extending in parallel to the scan lines Y1 and Y2. Therefore, each of the data lines X1 to X4 is connected to one of the video signal lines 17R, 17G, and 17B via the switching element 42 so that the video signal voltage VIDR, VIDG, and VIDB of the same color as the color emitted by the organic electroluminescent element 12 connected thereto can be supplied.
The period of the shift operation of the shift register 31 is a period in which the shift operation of the shift register 41 is performed to complete a selection of a scan line Yi and to initiate a selection of the next scan line Y(i+1) at a timing of the completion of selections of all of the data lines X1, X2, . . . , and Xn.
With the above-described structure, the shift operations of the shift register 31 and the shift register 41 allow all of the scan lines Y1, Y2, . . . , and Ym to be sequentially selected, and allow all of the data lines X1, X2, . . . , and Xn to be sequentially selected while the scan lines Y1 to Ym are selected, so that an image can be output using the entire display screen 20. One of the video signal voltages VIDR, VIDG, and VIDB is supplied to each of the data lines X1 to Xn from the corresponding video signal lines 17R to 17B when it is selected, and that video signal voltage VIDR, VIDG, or VIDB is charged in the holding capacitance 15 via the NMOS transistor 14 selected by the scan line Yi. The channel of the PMOS transistor 13 is controlled according to the charging state of the holding capacitance 15, so that a current which flows to each of the organic electroluminescent elements 12 from the common feeder lines 11 becomes a value corresponding to the video signal voltage VIDR, VIDG, or VIDB, thereby making it possible to cause the organic electroluminescent elements 12 to emit light at the desired brightness.